Conventionally, as the wavelength selecting switch, there has been proposed a wavelength selecting switch in which a dispersive element, a plurality of optical parts, and a micro electro mechanical systems (MEMS) array (a mirror array) are accommodated in a state of being sealed in an internal portion of a casing (for example, refer to patent document 1). In the wavelength selecting switch mentioned above, if a light path is appropriately adjusted so as to be fixed and the casing is sealed in a manufacturing stage, fluctuation of refraction factor due to change of air pressure can be avoided, and the light path within the casing is appropriately maintained.
FIG. 26 is an exploded perspective view showing an outline structure of a wavelength selecting switch disclosed in patent document 1. In the wavelength selecting switch, various optical parts constructing an optical system of the wavelength selecting switch are mounted to a flat optical bench 1000. Further, a casing 1001 is hermetically sealed by fixing the optical bench 1000 to which the optical system is mounted, to a bottom portion within the casing 1001, and covering an upper opening portion of the casing 1001 by a lid 1002.
Further, the wavelength selecting switch generally employs an apparatus which is provided with at least one input port, at least one output port, a dispersing portion, a converging portion and a deflecting portion. In this apparatus, the wavelength multiplexed light input into the wavelength selecting switch from one optical fiber of the input port is dispersed per wavelength by the dispersion portion such as a diffraction grating, and is converged into a different mirror element in the deflecting portion such as the MEMS mirror array. The light converged into each of the mirror elements is deflected and output in a predetermined output port direction per wavelength by controlling each of the mirror elements to a predetermined angle. Generally, the mirror array is constructed by mirror elements which are arranged in one line in a direction of x axis on a plane which is approximately vertical to the incident light. A light flux wavelength dispersed in the direction of x axis is incident on the mirror element. A wavelength of the light coming to a center of each of the mirror elements is preferably close to a predetermined value which is defined by a standard.
Further, as the dispersing portion, there has been various structures for obtaining a great dispersion by a reduced number of optical parts. For example, in a wavelength selecting switch having a dispersion portion of so-called Littman-Metcalf configuration in which the diffraction grating and the mirror are arranged in a mutually inclined manner, a great dispersing effect is obtained by converting the wavelength multiplexed light into parallel light by the lens or the mirror so as to enter into the diffraction grating, temporarily bringing the light dispersed by the diffraction grating to the mirror so as to be reflected, and thereafter again entering into the diffraction grating (for example, refer to patent document 2).
Patent Document 1: JP-A-2009-145887
Patent Document 2: U.S. Pat. No. 7,630,599